The Cryptosporidium is a waterborne parasitic protozoan responsible for the waterborne disease Cryptosporidiosis. Outbreaks of Cryptosporidiosis have been attributed to ingestion of drinking water, recreational water or food containing viable oocysts of Cryptosporidium. Cryptosporidium oocysts are typically introduced into the water through contamination of the water with fecal matter from cattle or humans containing oocysts. The oocysts have a hard outer cell wall that renders the oocysts resistant to the effects of chlorine present at concentrations typical of drinking water and recreational water. The oocysts are approximately 4-6 microns in size, which makes them difficult to remove by filtration. Since filtration and chlorination are universally practiced as a means for clarifying and sanitizing drinking water in municipal water treatment facilities and for maintaining the clarity of recreational water such as in swimming pools, water parks, hot tubs, baths and spas, the chlorine resistance and size of the oocysts make it difficult to ensure that water is free of this disease-causing microorganism.
A variety of filters and filter systems are used to clarify water in swimming pools, water parks, hot tubs and spas. Sand filters are common for swimming pool use and municipal water treatment. Diatomaceous earth filters are also available for use in swimming pools and water parks. Cartridge filters available to both pools and spas utilize a synthetic fabric enclosed in a plastic cartridge. Different filter media exhibit different capabilities for removing particles that vary in size. Sand filters are capable of filtering out particles in the size range of 25-50 microns, while cartridge filters are typically capable of removing particles in the size range of 15-25 microns. Diatomaceous earth filters exhibit the capability of removing particles in the size range of 5-10 microns, but have to be replaced frequently.
Coagulation and flocculation followed by filtration is commonly utilized in the treatment of drinking and recreational water to remove suspended microscopic particles. Some suspended microscopic particles tend to possess an electrostatic charge that prevents the particles from aggregating into larger filterable aggregates due to charge-charge repulsion. For example, bacteria and Cryptosporidium oocysts have a negative surface charge. This can be often overcome through the use of coagulants and flocculants. Coagulants are chemicals, that when dissolved in water, form ions of charge opposite to that of the suspended particles.
Flocculants are typically water soluble or water dispersible high molecular weight polyelectrolyte long chain polymers composed of repeating monomeric units that can be categorized into inorganic or organic compounds. The inorganic polyelectrolytes are polymerized metal salts and may include polyaluminum hydroxychloride, polyaluminum silicate sulfate and polyaluminum sulfate. Organic polyelectrolyte flocculants are derived synthetically or obtained from natural sources. The organic polyelectrolytes can exist as charged or uncharged polymers depending on their composition. Flocculants when added to water containing aggregates of microscopic particles or non-aggregated particles exhibit the ability to bind and gather the particles or particle aggregates into even larger aggregates that can be easily filtered.
It has also been suggested to treat recreational water possibly containing Cryptosporidium and/or Giardia by hyper-chlorination of the water. Hyper-chlorination is a process in which additional free chlorine is added to the recreation water such that the water contains free chlorine at a level generally above about 10-ppm; typically in the range of about 10-50 ppm. However, hyper-chlorination alone is effective in killing these parasites, in particular in killing Cryptosporidium but requires long contact times in presence of cyanuric acid. Cyanuric acid is used to stabilize the free chlorine against degradation by sunlight.
These treatments have not been successful in removing Cryptosporidium oocysts and/or Giardia cysts from recreational water, but requires the pool to remain closed to swimmers sometimes for days. As such, there is a need in the art for an effective method to remove Cryptosporidium and/or Giardia from the recreational water and to remove them in a manner which is cost effective, timely and easy to manage. The present invention provides an answer to that need.